The present invention relates to a method for separating tobacco particles on cigarette manufacturing machines. On cigarette manufacturing machines, the shredded tobacco particles are normally drop-fed from a feedbox on to a carding device and, from the latter, on to an essentially horizontal conveyor belt.
The latter, in turn, feeds the tobacco particles to a separating unit the function of which is to separate the lightweight tobacco particles, from which the cigarettes are made, from the heavier, woody ones consisting of the ribs from the processed tobacco leaves. The heavier particles are normally dropped into a reject collecting channel, whereas the lightweight particles are suction fed into a vertical channel closed off at the top by a suction conveyor belt.
On known types of separating devices, the method used for separating the lightweight particles from the heavier ones usually consists in setting up the output end of the said conveyor inside a chamber communicating, on one side, with the said vertical channel and, on the other, with the said reject channel, the latter channels usually being aligned with each other and having an air current blowing upwards through them. Thus, the lightweight particles are swept upwards along the said vertical channel, whereas the heavier particles drop down, against the current, along the reject channel.
For many types of tobacco, however, the abovementioned separating method has failed to keep the lightweight particle reject percentage within an acceptable margin. And not surprisingly since, on reaching the separating unit, the lightweight and woody particles are still closely bound together with the result that a considerable amount of lightweight particles is rejected together with the woody ones.
A known method of attempting to overcome this drawback consists in separating the heavier particles again as they fall down the reject channel, such separation usually being performed by hurling the heavier particles against the air current flowing up the reject channel. The abovementioned separating method is particularly effective when used on the separating device covered in British Pat. No. 2.096.876 on which the route travelled along by the heavy particles coming off the said conveyor is fitted with a baffle device for feeding the heavy particles into the reject channel against the air current with essentially no charge in kinetic energy. The impact between the high-speed heavy particles moving downwards and the air current blowing upwards produces a violent swirl inside the reject channel which separates the lighter tobacco strands from the woody particles.
Though more efficient than other known types of separating devices, the aforementioned known device still fails to separate all the woody particles from the lighter ones, a certain amount of which still manages to get rejected.
This drawback would appear to be caused by the excessive kinetic energy the heavier particles are possessed of when fed against the air current into the reject channel. In fact, on account of the speed they are travelling at, the woody particles always manage to carry some of the lighter particles clinging to them off to the reject channel.